1. Technical Field
The present invention relates to electro-optical devices including electro-optical elements, electronic apparatuses, and driving methods.
2. Related Art
A printer serving as an image forming apparatus includes a lighting device having multiple light-emitting elements arranged in an array, and the lighting device is used as a head unit for forming an electrostatic latent image onto an image carrier such as a photorecepter drum. The head unit is generally formed of a single line having a plurality of light-emitting elements arranged in a main scanning direction. One known light-emitting element is a light emitting diode such as an organic light emitting diode (OLED) element.
JP-A-8-39862 (see FIG. 6) discloses a technique in which a pulse width signal having a pulse width corresponding to a density data signal is generated and a driving current corresponding to correction data is supplied to light emitting diodes for a period of time corresponding to the pulse width of the pulse width signal. As shown in FIG. 11, a driving current is given by the sum of a reference current and a correction current, and gradation control is performed according to a pulse width T of the driving current.
The correction current is a current for correcting variations in threshold voltages of driving transistors or variations in light emitting characteristics of light emitting diodes, and is generally within a few percent of a reference current. Thus, the magnitude of the correction current is significantly smaller than the magnitude of the reference current. In general, it is difficult to realize a circuit capable of generating a small current with high accuracy. Even though such a circuit can be realized, there is a problem of increased circuit size.